The present invention generally relates the prediction of emissions from internal combustion engines and more particularly to a method for predicting NOx and HC emissions from an internal combustion engine and an engine control system that utilizes said method.
With increasingly strict regulations on the emissions of the internal combustion engine, automobile manufacturers are expending significant efforts to further reduce the levels of undesirable exhaust emissions. Unburnt hydrocarbons (HC) and oxides of nitrogen (NOx) are particularly important, as NOx emissions are known to be respiratory irritants and HC emissions that are heavier than methane and NOx emissions are known to aid in the formation of smog. While sensors for NOx and HC are known, such sensors are relatively expensive so vehicles are not routinely equipped with them for the direct measurement and corresponding control of NOx and HC emissions.
Furthermore, HC and especially NOx emissions were generally not considered to be predictable. For example, NOx is not produced in the combustion reaction, but rather results from the combustion reaction. At the elevated temperatures within a cylinder during a combustion event, dynamic nitrogen and oxygen molecules disassociate and recombine with one another to form NO and NO2. The mass of NOx that is formed depends on the temperature within the cylinder and the amount of time that the dynamic nitrogen and oxygen are subjected to the heat.
As such, many modern automobile manufacturers have based the control of an engine for emissions purposes on the amount of carbon dioxide that is produced during a combustion event. Because the combustion reaction is defined by a known chemical reaction, and because the amount of the reactants (i.e., air and fuel) input to the engine are known, the amount of carbon dioxide produced during a combustion event can be predicted with relatively high accuracy.
As those skilled in the art will appreciate, while NOx and HC emissions can be generally associated with the amount of carbon dioxide that is produced, such associations are not wholly accurate as they are highly focused on the chemical reaction and do not fully consider other aspects of the reaction, such as the amount of time available for the reaction. Accordingly, there remains a need in the art for a method by which combustion byproducts, such as NOx and HC may be more accurately predicted.
In one preferred form, the present invention provides a method for predicting a concentration of at least one undesirable exhaust emission discharged from an internal combustion engine that employs a charge of air and a charge of fuel for producing a combustion event that produces power. The method includes the steps of: determining a mass flow (m(a)) of the charge of air; determining a rotational speed (xcfx89) of the engine; determining a fuel-equivalence ratio (xcfx86) associated with the charge of air and the charge of fuel; and employing the mass flow (m(a)) of the charge of air, the rotational speed (xcfx89), the fuel-equivalence ratio (xcfx86) and an array of look-up tables to determine the concentration of the at least one undesirable exhaust emission.
The method of the present invention overcomes the aforementioned drawbacks by permitting the concentration of various undesirable exhaust emissions, such as NOx and/or HC, to be predicted with generally improved accuracy over a wide range of operating conditions. In a preferred form, intermediate terms are employed to greatly simplify the relationship between various engine parameters, such as rotational speed and mass air flow, to thereby permit the use of greatly simplified arrays of look-up tables that are readily incorporated into the memory of an engine controller.
In another preferred form, the present invention provides an engine control system for a motor vehicle having an internal combustion engine. The internal combustion engine utilizes a charge of air and a charge of fuel to support a combustion event that produces power and at least one undesirable exhaust emission. The engine control system includes a first sensor, at least one second sensor and an engine controller. The first sensor is coupled to the engine and operable for both sensing a rotational speed (xcfx89) of the engine and producing a first sensor signal in response thereto. The at least one second sensor senses at least one of a mass air flow and a throttle position and produces at least one second sensor signal in response thereto. The engine controller receives a plurality of sensor signals including the first sensor signal and the at least one second sensor signal wherein the plurality of sensor signals are indicative of an operating condition of the internal combustion engine so as to permit the engine controller to determine a mass flow (m(a)) of the charge of air, the rotational speed (xcfx89) and a fuel-equivalence ratio (xcfx86). The engine controller includes a memory having pre-programmed therein an array of look-up tables. The engine controller employs the mass flow (m(a)) of the charge of air, the rotational speed (xcfx89), the fuel-equivalence ratio (xcfx86) and the array of look-up tables to predict a concentration of the at least one undesirable exhaust emission that is generated during the combustion event.
The engine control system of the present invention overcomes the aforementioned drawbacks by permitting the concentration of various undesirable exhaust emissions, such as NOx and/or HC, to be relatively accurately predicted so that costly dedicated sensors, such as NOx sensors or smoke sensors, are not required.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.